Sucker rods normally come in 25 foot sections. Most conventional prior art sucker rods are simply solid rod stock with two male or male and female fittings at their ends. A single sucker rod, thus, according to this prior art, is simply an elongate solid rod having integral male fittings at both ends or one such and a female fitting at the other end. At the well site, these are joined, section by section, via couplings or the male and female fittings, to form a rod of great length sufficient to reach the length of the well casing and operate a pump at the bottom of the well. In oil wells, this pump reciprocates at the bottom of the well casing to force oil up the casing to the well head. A sucker rod assembly thus is an operating rod connected at its lower extremity to the pump element and, at its upper end, to the power motor and drive for the pump.
One problem well known to the art is that such sucker rods become so long in length that they stretch longitudinally and get out of synchronization with the reciprocation of the pump. Since some wells are 20,000 feet or more in depth, the sucker rod employed therewith is long indeed. In deep wells, the cumulative weight of the aggregate connected sucker rod elements becomes so great that different strength (and diameter) rods are required at different portions along the length of the rod in order to sustain the weight.
As may be seen from the prior art recited below, various solutions have been attempted to the problem of optimum sucker rod structure, function and design. These include the conventional solid rods, cable type or wire-including rods and pre-tensioned assemblies with sucker rod elements of various sorts. With respect to the latter, it is known to assemble a sucker rod having two main components, specifically, an outer compression tube and inner tension member which, when properly assembled, limit elongation of the device within certain load parameters and provide greater load carrying ability.
Another, but related problem is the question of electrical conductivity between elements of the sucker rod. This problem has at least two facets, specifically, first, the prevention of conductance between the sucker rods or sucker rod elements themselves and, secondly, the minimizing of conductive contact between the elements of the sucker rod chain and the well casing or well hole. Various attempts have been made in the prior art to deal with this problem.